Offer basic customizations

[sdirix]

• Header and Footer shall be given in as optional props. If given they shall replace the default ones. If null the respective component shall not be rendered at all
• By default only the React Preview shall be shown (when using the jsonforms-editor without customization). This preview shall also be exported.
• The jsonforms-editor takes additional {name, component} "editor" objects. When given, then the default react preview shall not be rendered. Instead each iof these components is rendered in a separate tab with the given name. Use this mechanism to integrate the angular preview via the app instead of the library. When given null only the editor is rendered.
• (Optional) The same customization can be done for the schema and uischema tabs, i.e. handing in {name, component} "palette" objects. If none are given the current ones are used by default.
• Unify the existing customizations (array vs object)
• Everything needed or useful for developing customizations should be exported via the root index.ts, for example the custom hooks.